Prostaglandin E2 and Its Receptor EP2 Modulate Macrophage Activation and Fusion in Vitro

The foreign body response (FBR) has impaired progress of new implantable medical devices through its hallmark of chronic inflammation and foreign body giant cell (FBGC) formation leading to fibrous encapsulation. Macrophages are known to drive the FBR, but efforts to control macrophage polarization remain challenging. The goal for this study was to investigate whether prostaglandin E2 (PGE2), and specifically its receptors EP2 and/or EP4, attenuate classically activated (i.e., inflammatory) macrophages and macrophage fusion into FBGCs in vitro. Lipopolysaccharide (LPS)-stimulated macrophages exhibited a dose-dependent decrease in gene expression and protein production of tumor necrosis factor alpha (TNF-α) when treated with PGE2. This attenuation was primarily by the EP4 receptor, as the addition of the EP2 antagonist PF 04418948 to PGE2-treated LPS-stimulated cells did not recover TNF-α production while the EP4 antagonist ONO AE3 208 did. However, direct stimulation of EP2 with the agonist butaprost to LPS-stimulated macrophages resulted in a ∼60% decrease in TNF-α secretion after 4 h and corresponded with an increase in gene expression for Cebpb and Il10, suggesting a polarization shift toward alternative activation through EP2 alone. Further, fusion of macrophages into FBGCs induced by interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GM-CSF) was inhibited by PGE2 via EP2 signaling and by an EP2 agonist, but not an EP4 agonist. The attenuation by PGE2 was confirmed to be primarily by the EP2 receptor. Mrc1, Dcstamp, and Retlna expressions increased upon IL-4/GM-CSF stimulation, but only Retnla expression with the EP2 agonist returned to levels that were not different from controls. This study identified that PGE2 attenuates classically activated macrophages and macrophage fusion through distinct EP receptors, while targeting EP2 is able to attenuate both. In summary, this study identified EP2 as a potential therapeutic target for reducing the FBR to biomaterials.